This article provides a brief overview of the standards in the field of web-mapping developed by the Open GIS consortium.

Convenience and simplicity of data presentation in the Internet environment is not in doubt at present. According to IWS, every year the number of Internet users is increasing by at least 200%, while in Russia the growth in Internet use was 664.5% in 2000-2005, and in the CIS as a whole - 2500%. However, until relatively recently, information transmitted over the network was represented only in small text or graphic formats. The restrictions on the type of information transmitted were mainly formed due to the maximum possible information transfer rate (the impossibility of transferring media files, large raster data, etc.) and the power of computers. However, Jacob Nielsen's Law, published in 1998, states that network bandwidth growth can best be approximated by an exponential curve and is in the order of 50% per year. In essence, this law is very similar to Moore's empirical law, formulated earlier (1965), showing that the complexity of a microcircuit device doubles every 24 months.

The most important consequence of the increase in the bandwidth and power of personal computers for the geographic information community is the broadest prospects for the presentation of spatial information in the global network. In this regard, various types of cartographic Internet services (such as /) are gaining increasing popularity.

Currently, general principles and standards in the field of software development that provide such services are developed and declared by the international non-profit organization Open GIS Consortium (OGC). The OGC was founded on September 25, 1994 and at the time of its creation had only 8 members. From 1992 to 2004, their number increased from 8 to 250, and today OGS represents the largest commercial, academic and government organizations engaged in the development or research in the development and development of geographic information or IT software (including such major corporations as Boeing , Oracle, ESRI, MapInfo, Intergraph, Google (membership since spring 2006) and many others).

In many ways, OGC's work in the field of geographic information systems can be compared with the W3C's work on standardizing processes and technologies in the world wide web. So, one of the first developments of OGC was the standards for the creation of GML - Geography Markup Language - an XML group language designed to describe geographically referenced objects. GML can be used both as a modeling language and as a language for transmitting spatial information in the network.

The OGC specifications offer the following types of web mapping services:

1. Web Map Service
   • determines the parameters for requesting and providing cartographic (spatial) information on the Internet in the form of a graphic image or a set of objects;
   • describes the conditions for obtaining and providing information about the contents of the map (for example, the properties of an object in a certain place on the map);
   • characterizes the conditions for obtaining and providing information about the capabilities of the server for the presentation of various types of cartographic information.
2. Web Feature Service
   • defines the conditions for receiving and updating georeferenced information by the client side of the application using the Geography Markup Language (GML);
   • describes a standard interface for accessing and manipulating geographic objects using the HTTP protocol.
3. Web Coverage Service
   • expands the capabilities of WMS to provide raster geographic information on the Internet;
   • Unlike WMS, the coverage service is designed to represent properties and values ​​at each specific point in the geographic space, and not to create ready-made pictures, and also allows data interpretation not on the server, but on the client side of the application.

It is on the basis of these specifications that most of the special software for the development of cartographic web services on the Internet is created. The number of applications that allow creating such services is growing every year, and in addition, along with paid software, the number of open source developments is growing, making it possible to create full-featured cartographic web services on a free basis just as easily and efficiently. To give a general idea of ​​the capabilities of WMS, we present a table prepared by OGC, which contains a summary of the various applications that support the OGS standards for web mapping, their functionality, browser support, integration with various data formats and estimated prices (this information is not official and to obtain accurate prices, you must contact the software developer or its distributors).

In recent years, the development of Internet technologies has increasingly begun to allow Internet users to use new means of delivery of information, including spatial information. Web mapping is a field of computer technology associated with the delivery of spatial data to the end user. We use the web prefix for convenience, any network can be used as a medium, not only the Internet. Of course, web cartography is one of the areas of geoinformation technologies in general.

The main tasks of web mapping are:

Visualization of existing information - spatial representation of information

Facilitation of work with spatial information on the web, search, routing and other services based on the location of objects (LBS - location based services).

The variety of modern mechanisms for creating web mapping applications is great. Let's try to give the simplest classification to the existing tools for developing such web applications. Of course, due to the fact that each manufacturer seeks to develop as comprehensive a tool as possible, including technologies for creating, visualizing and publishing data on the Internet, the classification we proposed can be considered rather arbitrary, nevertheless, it will allow the reader to navigate the ocean of existing solutions and proposals ...

Virtual globes (Google Maps, Google Earth, Virtual Earth, ArcGIS Explorer) are a simple and effective tool for quickly creating and publishing data on the Internet. This category of tools is characterized by massive distribution and fast delivery of data to users. They can use both a web browser and a separate application as a client. As a rule, they include access by default to a certain "substrate" - a database, which is both their big plus and no less minus, since in most cases it is impossible to change this substrate. Also, as a rule, these tools are characterized by problems when working with large amounts of user data, customizability, elementary analysis (cropping, intersection of data layers).

Custom GIS (ArcGIS, Mapinfo, QGIS, gvSIG) is a large and complex category closely related to web mapping. As a rule, custom GIS, on the one hand, play the role of clients working with data supplied by cartographic web servers (usually by WxS, see below), and on the other hand, they carry out mass preparation and analysis of data before publishing it on the web.

Map web servers (MapServer, GeoServer, OpenLayers, etc.) are a whole family of free and proprietary products designed for quick publication of user data on the web. These tools allow you to create an interface of the required complexity, integrate the service with a database that supports spatial data classes (PostgreSQL, SQL Server, MySQL, ArcSDE). The main difference between such systems and Google Maps is complete control over the software and the data itself, but in return you have to pay with the greater complexity of installation and configuration, which often requires at least basic knowledge of programming languages ​​(javascript, php) and the basics of administration.

A special type of tool that is emerging more recently is custom GIS integrated with virtual globes, which serves as one way of presenting data.

Map web servers (MapServer, GeoServer, OpenLayers, etc.) are a whole family of free and proprietary products designed for quick publication of user data on the web. These tools allow you to create an interface of the required complexity, integrate the service with a database that supports spatial data classes (PostgreSQL, SQL Server, MySQL, ArcSDE). The main difference between such systems and Google Maps is complete control over the software and the data itself, but in return you have to pay with the greater complexity of installation and configuration, which often requires at least basic knowledge of programming languages ​​(javascript, php) and the basics of administration.

GeoServer is an open source server for managing and accessing geographic information systems (GIS) data sources using Web Feature Service (WFS) and Web Map Service (WMS). It includes a rich REST API for managing complex Web application data at runtime without manual intervention, and integrates well with the OpenLayers mapping tool. It also supports the WFS-T service for updating live data, as well as Geographic Markup Language (GML), Keyhole Markup Language (KML), and many other formats. Data is organized into workspaces and data stores using disk storage or PostGIS. Using the built-in REST API, you can manipulate datasets in real time. This software also includes a ready-to-use web interface.

Additional Information

WMS is the interface for the requested map images and WFS is the interface for the requested vector map data. WMS is more often used in situations where the purpose is solely to display data. WFS is more convenient when users interact with the source data (for example, querying the values ​​of an attribute table or modifying data). The WFS modification is often referred to as WFS-T or WFS with transactions.

OpenLayers is an excellent client-side JavaScript mapping tool that lets you develop (closely with GeoServer) Web applications to represent spatial data. For information on OpenLayers, read the article Combining Data with OpenLayers.

it introduces a simple XML editor.

Using uDig to Create Simple Styles

January 17, 2012 at 01:35 PM

DIY web mapping service. Part 1: Overview of the toolkit

• M2M Ukraine blog

Hello!
Until a certain point, the tasks of displaying data on a map on the Internet can be solved using quite powerful web mapping tools such as Google Maps API, Yandex.Maps API, OpenStreetMap API.

When there are a lot of objects, the development rests on the client's performance, since the computing power of the computer of the person who uses the map is spent on rendering. In addition, the "artistic" capabilities of such services are not always sufficient for the location of the necessary information on the map.

To solve these problems, the server-side mapping software is used, which provides more opportunities.

In this series of articles, we will look at installing and configuring a web service that will display various geo-data on a map.

Formulation of the problem

Let's take a fairly relevant and mundane task of displaying objects that are stored in a database. The data source will be a geo-field in the PostgreSQL database. On the server side, we need to generate a layer with objects and overlay it on Google Maps. It is also necessary to perform all operations on free software with the ability to finish it for your own needs. It is also necessary to avoid using third-party map services as much as possible.

Tools

To solve our problem, it is necessary to represent the principle of operation of the entire bundle, therefore, consider the diagram:

Different formats of incoming data can be used depending on the GIS web server. In our case, we will be using MapServer which can use vector and raster data.

The data source must be prepared in advance, which means that you need to take coordinates from any gps device and import them into the database or into any other format that MapServer supports. In our case, we will take data from ours, which, through the gprs channel, adds points to the server in the PostgreSQL database.

PostgreSQL was chosen because it has a wonderful PostGIS shim that allows you to run geo-queries from the database. For example, select areas that intersect the route.

In geodesy, there is such a thing as projection. Projection is a mathematically defined way of mapping the surface of an ellipsoid onto a plane. Those. how the globe will be laid out on a flat map. There are a lot of projections, the data that will be imported into the database may be in one projection and we will need to display them in another, for this, together with MapServer, we will need to install the PROJ library on the server, which will help us work with projections.

The MapServer itself is configured by a map file, in which we describe exactly how we need to display data, where to get it, and how to color the map itself, how roads, routes, etc. will look like.

In total, it turns out that, at a specific request, MapServer through PostGis using PROJ selects data from PostgreSQL and outputs it in one of the specified formats, from a regular image to WMS (which we will use to organize a web service). At the same time, all this is regulated by the configuration map file, which indicates to the server what information from where to get it.

MapServer works in conjunction with Apache and outputs information to the browser. We are interested in the MapServer - WMS mode of operation. In this mode, the client program (desktop or, for example, Google API through a special function), using a GET request, asks to show MapServer tiles with certain coordinates, sizes and transparency. In response to such a request, MapServer returns images that the client program uses to overlay the map.

If we leave the chosen way of the service for our task, then the following tools will remain in the bottom line:

Conclusion

With the help of PostgreSQL / PostGis + MapServer + Google Maps, we can solve most of the tasks that webmasters face today when organizing their own geo-service, and in particular our task of displaying points on Google maps.

In the second part, we will look at installing MapServer and PostgreSQL / PostGis, as well as linking them together.

Geographers know that communication is one of the most “geographic” branches of the economy. Now it is becoming an instrument for integrating the economic activity of states around the world, a means of its internationalization. NV Alisov even proposed to single it out as a special scientific direction.

Today, before our eyes, a new information space is being formed, and its significant subdomain is the geoinformation space, that is, the environment in which digital geo-information and geo-images of various types and purposes function. Internet users quickly appreciated the new possibilities for interactive mapping. One of the most accessible options is the creation of cartograms and cartodiagrams based on statistical data. In this case, no special processing of the initial information is required, it is enough to have a statistical database and a cartographic base with a grid of administrative division of the territory. Even the term "interactive map composition" has appeared.

More complex thematic maps require a special search and selection of sources, their combination and combination, involving different databases, performing selection procedures, generalization and classification, selection of image methods, etc. To show dynamics, animation tools are used, a sound series is added.

For a number of countries, schematic maps of the structure of networks belonging to different telecommunications companies or scientific communities have been created. For example, in Russia there are maps of telecommunication networks of three levels: all-Russian, regional and local (for some scientific institutes and universities).

The plots of maps of telecommunication networks are very diverse. These are the placement of lines, channels, communication centers and the network structure as a whole, the amount of information passing per unit of time, the degree of loading by months, weeks, days, the number of calls, types of requests, the intensity of information flows, etc.

The maps can also represent such technical indicators as bandwidth, availability, speed and cost of information transfer. Thus, mapping becomes a useful tool for planning development, optimizing the location and operation of networks.

For each country, and for Russia in particular, the development of computer networks has a double meaning: on the one hand, it is the ability to access the vast and varied information accumulated by the world community, and on the other, the inclusion of its own information, including geographical and cartographic, resources in the world scientific and practical circulation

Electronic atlases occupy a special place on the Internet. They turned out to be a successful alternative to paper atlases, the creation of which, as is known, takes a long time, sometimes many years, so that some capital scientific and reference atlases are partially outdated even in the process of preparation.

Currently, there are several types of electronic atlases: some of them are intended only for visual viewing (“flipping”); in others, it is possible to change the design, methods of displaying and even classify the phenomena being mapped, as well as to enlarge and reduce the image, to obtain paper copies of maps (so-called "interactive atlases"); still others allow you to work more variedly with maps, combine and compare them, perform quantitative analysis and assessment on maps, perform overlays of maps (overlays) and spatial correlations. Essentially, these are Atlases. Finally, there are special electronic Internet atlases, in the structure of which, in addition to maps, additional information and means of interactive actions, there are necessarily also means of "navigation", that is, moving around the network in search of additional information or other maps.

In recent years, the issue of "publishing national atlases on the Internet" has been discussed. We are talking about placing atlases on a computer network and, of course, first of all, capital atlases, which can be constantly updated as information becomes available, for example, from the state statistical service. Thus, there is a continuous "watch" on the atlas, a kind of tracking (monitoring), and national atlas information systems are formed, which can be used by institutions and individuals with personal computers of any type.

National electronic atlases have been created or are in the process of being created in the Netherlands, China, and other countries. As a rule, they are based on multivolume paper atlases. Thus, the national atlas of Sweden includes 17 volumes - 20 volumes, Finland - 25 issues - 40 issues. True, electronic atlases do not always repeat their paper prototypes, since the maps are constantly updated, new plots appear, and even the structure is partially changed.

The draft National Atlas of Russia envisages, along with the traditional 10-volume printed edition, the creation of two more versions: 1st - electronic (simplified) on magnetic floppy disks and CDs; it is being developed virtually simultaneously with the traditional paper version and can subsequently be supplemented with video and audio information, animations and hypertext; 2nd - GIS-version, which is also supposed to be expanded with the help of multimedia and placed in computer networks.

The abundance of cards and others circulating on the Internet is not only a blessing, but also a big problem for the user. The information is overwhelming, it is sometimes difficult for the user to navigate and find what he needs. Graphic documents are redundant and not always organized. As one English cartographer aptly put it, turning to the Internet is sometimes like trying to get drunk from a fire hose. Therefore, the most important problem is the creation of convenient navigators - guidebooks that allow you to move in an electronic network along logically connected routes in search of the required geo-image, as well as a friendly user interface - a tool that provides simple and convenient communication with the network.

One of the means of organizing information on the Internet is the creation of virtual atlases. These are, as it were, "non-existent" atlases, which, however, can be formed under certain conditions, applying certain rules for working on the Internet. In fact, a virtual atlas is a user graphical interface - a tool for working with maps, aerial and space images, animations, other geo-images, texts, sounds, statistical data, all kinds of pointers and other spatial information. The first virtual atlas was created by Australian cartographers and is intended for schoolchildren. It gives access to spatial data of different levels of the global overview to the country or region.